The present invention relates to a liquid heating apparatus of, for example, a food frying machine, noodle boiling equipment, etc., and in particular a liquid heating apparatus which is able to efficiently heat liquid in a liquid tank.
Conventionally, a food frying machine acting as a liquid heating apparatus for frying foods with edible oil stored in an oil reservoir is disclosed by, for example, Japanese Laid-open Utility Model No. 64837 of 1986. The food frying machine 51 is, as shown in FIG. 11 (PRIOR ART), such that a reservoir portion 54 which accumulates sediment remaining in an oil tank 52 is formed so as to protrude downward from one end side of the bottom 53 of the oil tank 52, a concave heat leading passage 56 which leads heat from a burner 55 is formed so as protrude upward along the lengthwise direction of the rear side of the bottom 53 of the oil tank 52, and a fin 57 having a cross-shaped section is fixed in the heat leading passage 56.
Another conventional example is disclosed by, for example, Japanese Laid-open Utility Model No. 45046 of 1986. The food frying machine 151 is, as shown in FIG. 12 (PRIOR ART), composed of a burner 154 disposed downward of a roughing flat bottom 153a of an oil tank 153 accommodated and disposed in the casing 152, and a combustion chamber 156 which heats oil 155 in the oil tank 153 by the burner 154, wherein a reservoir portion 157 which accumulates sediment in the oil tank 153 is formed so as to protrude downward in the direction from the bottom portion 153a of the oil tank 153 toward the combustion chamber 156, a heat insulating member 158 is provided at the surrounding of the reservoir portion 157, and a fin 159, which protrudes toward the combustion chamber 157, is provided at the bottom portion 153a. 
However, in the food frying machine 51, since a fin 57 can not be fixed close to the bottom portion 53, there is a problem in that sufficient heat efficiency can not be obtained. That is, since the food frying machine 51 has such a structure that the fin 57 is formed by uniting two long plate members so that the cross section thereof is cross-shaped, and the fin 57 is disposed in a concave heat leading passage 56 on the bottom portion 53, it is difficult for the fin 57 to be directly fixed inside the heat leading passage 56.
Furthermore, even though the fin 57 is fixed directly inside the heat leading passage 56, the contact area between the fin and the interior of the heat leading passage 56 is only equivalent to the plate thickness of the two plate members, and in a case where the fin 57 is directly fixed, there is a possibility that the fin 57 is warped in the lengthwise direction due to heat expansion to cause the bottom portion 53 of the oil tank 52 to be deformed. Therefore, the fin 57 must be fixed with appointed space remaining between the outer circumferential end of the fin 57 and the interior of the heat leading passage 56, wherein the heat transmission area made effective by the fin 57 can not be made large, and it becomes difficult to obtain sufficient heat efficiency.
Furthermore, since the fin 57 itself is complicated and is cross-shaped in its cross section, the production cost thereof is increased, and since it is necessary to form a concave heat leading passage 56 at the bottom portion 53 of the oil tank 52, the production cost of the oil tank 52 is also increased, and therefore causes a problem in that the structure of the food frying machine 51 itself is complicated and the production cost thereof is accordingly increased.
Furthermore, since the fin 57 having a cross-shaped section is disposed in the heat leading passage 56 in a fixed state, it becomes difficult to eliminate soot or the like which is adhered to the deep side (upward side) of the heat leading passage 56 of the fin 57, wherein cleaning work of the burner portion 55 is made cumbersome, and since the bottom portion 53 of the oil tank 52 is made roughly horizontal, the sediment is deposited on the bottom portion 53, and become cumbersome to eliminate the sediment. That is, there is a problem in that the maintenance of a food frying machine 51 itself is not easily carried out.
Furthermore, in a food frying machine 151 according to another conventional example, since a combustion gas passage 160 communicating with the combustion chamber 156 is merely installed downward of the bottom portion 153a of the oil tank 153 and rearward of the rear portion 153b, it is difficult to cool down the outside plate member 160a of the combustion gas passage 160, wherein the outside plate of the casing 152 is apt to be highly heated. In particular, the rear surface plate 152a of the casing 152 is disposed roughly close to the outside plate member 160a of the combustion gas passage 160 formed outside the rear portion 153b of the oil tank 153. Therefore, the temperature of the outside plate member 160a is directly transmitted to the rear surface plate 152a, wherein the temperature thereof is apt to be highly increased.
As a result, in a case where such a food frying machine 151 is installed for use at a cooking place, there is a fear that the temperature of the left and right side plates and upper surface plate, which are connected to the rear side plate 152a of the casing 152 is raised to such a degree that a user can not touch the machine with his hand, and in particular since the temperature of the rear side plate 152a of the casing 152 is apt to be raised, vacant space of an appointed interval is required rearward of the casing 152, whereby such a problem arises, by which the installation space was developed in view of the abovementioned shortcomings and problems, and it is therefore an object of the invention to provide a liquid heating apparatus which is cheap in its production cost with a simplified structure, by which easy maintenance can be secured, wherein fins are fixed directly to the bottom portion of the liquid tank to secure sufficient heat efficiency.
Another object of the invention is to provide a liquid heating apparatus in which a temperature rise of the outside plate of the casing is efficiently suppressed by effectively cooling the plate members which form a combustion gas passage, and the installation space efficiency can be improved.
In order to achieve the abovementioned objects, one aspect of the invention is characterized in that, in a liquid heating apparatus which raises the temperature of liquid in a liquid tank by heating the bottom of the liquid tank with a burner disposed downward of the bottom of the liquid tank, an inclination plane is inclined at an appointed predetermined degree of angle and is formed on the bottom of the liquid tank, long fins are fixed on the rear side of the inclination plane along the inclination direction thereof, and the fins are provided with thermal expansion absorbing means, which are able to absorb thermal expansion, along the lengthwise direction thereof.
With such a construction, the temperature of liquid is raised in line with the inclination plane of the bottom portion of the liquid tank being heated by combustion of a burner while the combustion gas of the burner is caused to flow through the fins fixed at the rear side of the heating surface along the inclination plane. Since the fins are fixed by a thermal expansion absorbing means in a state where the fins are closely adhered to the rear side of the inclination plane, at least the fixed portion thereof becomes a heat transmission portion to increase the transmission area, whereby heat efficient fins are provided so as to protrude from the rear side of the inclination plane. Therefore, the shape of the fins is simplified to make maintenance easy.
Furthermore, the fins can be formed to be roughly channel-like in their cross section, and the bottom wall portion can be adhered to and fixed at the rear side of the inclination plane of a liquid tank. With such a construction, since the bottom wall portion of the fins having a channel-like section is adhered to and fixed at the rear side of the inclination plane, a sufficient heat transmission area from the fins to the inclination plane can be obtained, and the side wall portions at both sides of the bottom wall portion also become heat transmission portions, thereby causing the heat receiving area to be increased, wherein heat efficiency is further increased.
The thermal expansion absorbing means can be slits formed at the side wall portions protruding from the rear side of the inclination plane of the fins. The thermal expansion absorbing means can also be provided in the form of differences in the protrusion dimension of both end portions in the lengthwise direction of the side wall portions protruding from the rear side of the inclination plane of the fins.
With such a construction, the thermal expansion of the fins can be absorbed by the slits formed at an appointed interval along the lengthwise direction of the fins and differences in the protrusion dimension of both end portions in the lengthwise direction of the fins, whereby warping, etc., of the fins in the lengthwise direction can be prevented from occurring, wherein the fins are fixed close to the inclination plane, and the heat transmission area is increased to improve heat efficiency.
A low temperature portion protruding downward of the inclination plane can be provided on the bottom of the liquid tank. With such a construction, since sediment naturally drops on the inclination plane and is accumulated in the low temperature portion, the sediment is not heated, and the liquid in the liquid tank can be prevented from deteriorating in quality. In addition, since it becomes easy to clean up the bottom of the liquid tank, maintenance can be made further easy.
By employing one construction of the invention, combustion gas can be generated in line, with the combustion gas heating the bottom of the liquid tank with the heat flowing from the upstream side to the downstream side in the combustion gas passage. The combustion gas passage is raised by flow of the combustion gas. However, the plate member is cooled down by cooling air flowing in the cooling air passage formed outside thereof.
Since the downstream side of the cooling air passage and the downstream side of the combustion gas passage are joined to each other, the cooling air in the cooling air passage is absorbed by a draft generated by the difference in temperature at the confluence. By the absorption force, it is possible to increase the flow quantity of cooling air flowing in the cooling air passage while the burner is in combustion, the outside plate member of the combustion gas passage is effectively cooled, wherein the temperature rise of the outside plate of the casing, which is disposed outside the cooling air passage, is suppressed, and there is no need to provide wide vacant space rearward of the casing when installing the apparatus. Therefore, installation space efficiency can be improved.
The confluence of the combustion gas passage and the cooling air passage can be provided at the upper part of the rear side of the liquid tank. With such a construction, since it is possible to release the combustion gas and cooling air into the atmosphere at the upper part of the rear side of the liquid tank, the temperature rise of the rear side plate of the casing can be further suppressed.
The opening at the upstream side of the cooling air passage can be provided at the bottom portion of the casing which accommodates and arranges the liquid tank. With such a construction, since the temperature on the floor in a cooking place, on which this type of a liquid heating apparatus is installed, is generally lowered due to use of water, air (cool air) on the floor whose temperature is low can be taken in through the opening at the bottom portion of the apparatus, and the cooling effect of the combustion gas passage can be further increased.
The above and other advantages of the invention will become apparent in conjunction with the accompanying claims and drawings wherein like reference numerals refer to like parts.